1. Field of the Invention
This invention relates to electronic engine controls for an internal combustion engine. In particular, it relates to the use of sensors positioned in a gas stream and providing a signal indicating operating conditions of the engine.
2. Prior Art
Electronic engine control of an internal combustion engine is known. That is, operating conditions of the internal combustion engine are controlled by an electronic engine control module in response to sensing of various engine parameters.
For example, one parameter to be sensed is the amount of oxygen in the exhaust gas flow. To this end, an exhaust gas oxygen sensor is placed in the exhaust gas stream from the engine.
Operation of the exhaust gas sensor produces an output which is used to control air fuel ratio. The sensor produces a more accurate indicator of oxygen concentration when operating within a certain temperature range. To provide such a desired temperature range for the sensor it is known to use a heater for the oxygen sensor. It would be desirable to achieve this desired temperature range quickly. These are some of the problems this invention overcomes.
To protect such oxygen sensors it is known to provide a protection tube around the sensing element in the exhaust gas flow. However, for fast light-off of the sensor, in less than ten seconds, the engine is started and the oxygen sensor heater is powered up. During such a start of the engine, water, fuel or liquid particles in the exhaust gas flow could damage the oxygen sensor element and the protection tube. That is, when the heater is turned on, the sensing element and protection tube will heat up rapidly. When water particles in the exhaust gas flow come in contact with the sensing element, thermal shock could cause cracks in the ceramic especially at the colder ambient temperatures.